scholarly journals Effects of repetitive pulsing on multi-kHz planar laser-induced incandescence imaging in laminar and turbulent flames

2015 ◽  
Vol 54 (11) ◽  
pp. 3331 ◽  
Author(s):  
James B. Michael ◽  
Prabhakar Venkateswaran ◽  
Christopher R. Shaddix ◽  
Terrence R. Meyer
Keyword(s):  
Turbulent Flames ◽  
Planar Laser ◽  
Laser Induced Incandescence

scholarly journals High-speed, three-dimensional tomographic laser-induced incandescence imaging of soot volume fraction in turbulent flames

2016 ◽  
Vol 24 (26) ◽  
pp. 29547 ◽  
Author(s):  
Terrence R. Meyer ◽  
Benjamin R. Halls ◽  
Naibo Jiang ◽  
Mikhail N. Slipchenko ◽  
Sukesh Roy ◽  
...  
Keyword(s):  
High Speed ◽  
Volume Fraction ◽  
Three Dimensional ◽  
Soot Volume Fraction ◽  
Turbulent Flames ◽  
Laser Induced Incandescence

Filtered Rayleigh Scattering Thermometry in a Premixed Sooting Flame

Volume 4 ◽  
2004 ◽  
Author(s):  
Sean P. Kearney ◽  
Thomas W. Grasser ◽  
Steven J. Beresh
Keyword(s):  
Rayleigh Scattering ◽  
Volume Fraction ◽  
Imaging Techniques ◽  
Soot Volume Fraction ◽  
Image Data ◽  
Molecular Iodine ◽  
Line Center ◽  
Temperature Imaging ◽  
Planar Laser ◽  
Laser Induced Incandescence

Filtered Rayleigh Scattering (FRS) is demonstrated in a premixed, sooting ethylene-air flame. In sooting flames, traditional laser-based temperature-imaging techniques such linear (unfiltered) Rayleigh scatting (LRS) and planar laser-induced fluorescence (PLIF) are rendered intractable due to intense elastic scattering interferences from in-flame soot. FRS partially overcomes this limitation by utilizing a molecular iodine filter in conjunction with an injection-seeded Nd:YAG laser, where the seeded laser output is tuned to line center of a strong iodine absorption transition. A significant portion of the Doppler-broadened molecular Rayleigh signal is then passed while intense soot scattering at the laser line is strongly absorbed. In this paper, we demonstrate the feasibility of FRS for sooting flame thermometry using a premixed, ethylene-air flat flame. We present filtered and unfiltered laser light-scattering images, FRS temperature data, and laser-induced incandescence (LII) measurements of soot volume fraction for fuel-air equivalence ratios of φ = 2.19 and 2.24. FRS-measured product temperatures for these flames are nominally 1500 K. The FRS temperature and image data are discussed in the context of the soot LII results and a preliminary estimate of the upper sooting limit for our FRS system of order 0.1 ppm volume fraction is obtained.

Two-dimensional imaging of ignition and soot formation processes in a diesel flame

2005 ◽  
Vol 6 (1) ◽  
pp. 21-42 ◽  
Author(s):  
H Kosaka ◽  
T Aizawa ◽  
T Kamimoto
Keyword(s):  
Soot Formation ◽  
Diesel Spray ◽  
Oxidation Reactions ◽  
Soot Particles ◽  
Nozzle Orifice ◽  
Spray Flame ◽  
Soot Precursor ◽  
Planar Laser ◽  
Laser Induced Incandescence ◽  
Ambient Gas

The processes of ignition and formation of soot precursor and soot particles in a diesel spray flame achieved in a rapid compression machine (RCM) were imaged two-dimensionally using the laser sheet techniques. For the two-dimensional imaging of time and of location where ignition first occurs in a diesel spray, planar laser-induced fluorescence (PLIF) of formaldehyde was applied to a diesel spray in an RCM. Formaldehyde has been hypothesized to be one of the stable intermediate species marking the start of oxidation reactions in a transient spray under compression ignition conditions. In this study, the laser-induced fluorescence (LIF) images of the formaldehyde formed in a diesel fuel spray during the ignition process have been obtained by exciting formaldehyde with the third harmonic of a neodymium-doped yttrium aluminium garnet (Nd:YAG) laser. The LIF images of formaldehyde in a spray revealed that the time when the first fluorescence is detected is almost identical with the time when the total heat release due to low-temperature oxidation reactions equals the heat absorption by fuel vaporization in the spray. The formaldehyde level rose steadily until the high-temperature reaction phase of diesel spray ignition. At the start of this ‘hot-ignition’ phase, the formaldehyde concentration fell rapidly, thus signalling the end of the low-temperature ignition phase. Increases in the initial ambient gas temperatures advanced the hot-ignition starting time. The first hot ignition occurred in the periphery of spray head at initial ambient gas temperatures between 580 and 660 K. When the ambient gas temperature was increased to 790 K, the position of the first ignition moved to the central region of the spray head. For the investigation of soot formation processes in a diesel spray flame, simultaneous imaging of the soot precursor and soot particles in a transient spray flame in an RCM was conducted by PLIF and by planar laser-induced incandescence (PLII) techniques. The third harmonic (355 nm) and the fundamental (1064 nm) laser pulses from an Nd:YAG laser, between which a delay of 44 ns was imposed by 13.3 m of optical path difference, were used to excite LIF from the soot precursor and laser-induced incandescence (LII) from soot particles in the spray flame. The LIF and the LII were separately imaged by two image-intensified charge-coupled device cameras with identical detection wavelengths of 400 nm and bandwidths of 80 nm. The LIF from the soot precursor was mainly located in the central region of the spray flame between 40 and 55 mm (between 270 and 370 times the nozzle orifice diameter d°) from the nozzle orifice. The LII from soot particles was observed to surround the soot precursor LIF region and to extend downstream. The first appearance of the LIF from the soot precursor in the spray flame preceded the appearance of the LII from soot particles. The intensity of the LIF from the soot precursor reached its maximum immediately after rich premixed combustion. In contrast, the intensity of the LII from soot particles increased gradually and reached its maximum after the end of injection. Measured LIF spectra, of the soot precursor in the spray flame, were very broad with the peak between 430 and 460 nm.

Understanding the soot reduction associated with injection timing variation in a small-bore diesel engine

2019 ◽  
pp. 146808741986805 ◽  
Author(s):  
Lingzhe Rao ◽  
Yilong Zhang ◽  
Sanghoon Kook ◽  
Kenneth S Kim ◽  
Chol-Bum Kweon
Keyword(s):  
Diesel Engine ◽  
Fuel Injection ◽  
Soot Formation ◽  
Soot Oxidation ◽  
Laser Induced Fluorescence ◽  
Injection Timing ◽  
Gas Temperature ◽  
Planar Laser ◽  
Laser Induced Incandescence ◽  
Ambient Gas

This study shows the in-cylinder soot reduction mechanism associated with injection timing variation in a small-bore optical diesel engine. For the three selected injection timings, three optical-/laser-based imaging diagnostics were performed to show the development of high-temperature reaction and soot within the cylinder, which include OH* chemiluminescence, planar laser–induced fluorescence of hydroxyl and planar laser–induced incandescence. In addition, detailed soot morphology analysis was conducted using thermophoresis-based soot particle sampling from two locations within the piston bowl, and the subsequent analysis of transmission electron microscope (TEM) images of the sampled soot aggregates was also conducted. The results suggest that when fuel injection timing is varied, ambient gas temperature makes a predominant effect on soot formation and oxidation. This is primarily combustion phasing effect as the advanced fuel injection moved the start of combustion closer to the top dead centre, and therefore, soot formation and oxidation occurred at elevated ambient gas temperature. There was an overall development pattern of in-cylinder soot consistently found for three injection timings of this study. The planar laser–induced incandescence images showed that a few small soot pockets first appear around the jet axis, which promptly grow into large soot regions behind the head of the flame marked planar laser–induced fluorescence of hydroxyl. The soot signals disappear due to significant oxidation induced by surrounding OH radicals. When the injection timing is advanced, the soot formation becomes higher as indicated by higher total laser–induced incandescence coverage, increased sampled particle counts and larger and more stretched soot aggregate structures. However, soot oxidation is also enhanced under this elevated ambient temperature environment. At the most advanced injection timing of this study, the enhanced soot oxidation outperformed the increased soot formation with both peak laser–induced incandescence signal coverage and late-cycle coverage showing lower values than those of more retarded injection timings.

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